Each participant will have three data collection periods. Each data collection period will last one shift rotation (5 -7 days): One 5-shift or 7-shift block of Orbit 1 night shifts on console with access to photic and exercise countermeasures, a second 5-shift or 7-shift block of Orbit 1 night shifts on console with no access to countermeasures, and a third 5-shift block of daytime office work off console. We will be measuring sleep via a wrist worn activity measuring device and compliance of exercise intervention via a small, commercially available heart monitor worn around the chest underneath clothing. The activity device will be worn continuously and the heart monitor will be worn on shift. These devices will be downloaded at the end of each block of shifts. Subjects will complete a short baseline questionnaire once at the beginning of the study. Subjective alertness will be assessed with the Karolinska Sleepiness Scale (KSS), performance testing will occur regularly and 'end of shift' questionnaires will be completed at the end of each shift. Drowsiness will be measured on the commute to and from work with the Optalert.